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The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite mission led by Professor Charles L. Bennett of Johns Hopkins University, whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. The satellite was launched by a Delta II rocket on June 30, 2001, at 3:46 p.m. EDT from Cape Canaveral Air Force Station, Florida, USA.

WMAP was the Breakthrough of the Year for 2003 according to Science magazine.[1] Mission results papers were #1 and #2 on the list of "Super Hot Papers in Science Since 2003."[2]

The goal of WMAP is to map out minute temperature differences in the Cosmic Microwave Background (CMB) radiation in order to help test theories of the nature of the universe. It is the successor to COBE and one of the series of medium-class explorer (MIDEX) satellites.

WMAP is named after Dr. David Wilkinson, a member of the science team and pioneer in the study of cosmic background radiation. The science goals of the WMAP broadly dictate that the relative CMB temperature be measured accurately over the full sky with high angular resolution and sensitivity. The overriding priority in the design was the need to control systematic errors in the final maps. The specific goal of WMAP is to map the relative CMB temperature over the full sky with an angular resolution of at least 0.3°, a sensitivity of 20 µK per 0.3° square pixel, with systematic artifacts limited to 5 µK per pixel.

To achieve these goals, WMAP uses differential microwave radiometers that measure temperature differences between two points on the sky. WMAP observes the sky from an orbit about the L2 Sun-Earth Lagrangian point, 1.5 million km from Earth.

This vantage point offers an exceptionally stable environment for observing, since the observatory can always point away from the Sun, Earth and Moon while maintaining an unobstructed view to deep space. WMAP scans the sky in such a way as to cover ~30% of the sky each day and as the L2 point follows the Earth around the Sun WMAP observes the full sky every six months. To facilitate rejection of foreground signals from our own Galaxy, WMAP uses five separate frequency bands from 22 to 90 GHz.

On February 11, 2003, NASA issued a press release regarding the age and composition of the universe. This release included the "best baby picture" of the universe taken up to that point. According to NASA, this picture "contains such stunning detail that it may be one of the most important scientific results of recent years". The new data far exceeded previous CMB measurements in both accuracy and precision.

The three-year WMAP data were released at noon on March 17, 2006. The data included temperature and polarization measurements of the CMB, which provided further confirmation of the standard flat Lambda-CDM model and new evidence in support of inflation.

Contents 1 Findings so far from WMAP 2 Other Instruments for measuring fluctuations in the Cosmic Microwave Background 2.1 Earlier 2.2 Later 3 References 4 See also 5 External links

WMAP provided much higher accuracy measurements of many cosmological parameters than had been available from previous instruments. According to current models of the universe, WMAP data show:

• The universe is 13.7 ± 0.2 billion years old.^[1]
• The universe is composed of:
  • 4% ordinary baryonic matter
  • 22% an unknown type of dark matter, which does not emit or absorb light.
  • 74% a mysterious dark energy, which acts to accelerate expansion.
• The cosmological scenarios of cosmic inflation are in better agreement with the three-year data, although there is still an unexplained anomaly on the largest angular measurement of the quadrupole moment.
• The Hubble constant is 70 (km/s)/Mpc, +2.4/-3.2
• The data are consistent with a flat geometry, with Ω = 1.02 +/- 0.02.
• CMB polarization results provide experimental confirmation of cosmic inflation favoring the simplest versions of the theory.
• WMAP cold spot : a huge hole in the Universe, nearly a billion light-years across ^[2]

Main article: Cosmic microwave background experiments

Before WMAP, there were several incremental improvements in our maps of the Cosmic Microwave Background:

• COBE - measured the very large scale fluctuations
• Cosmic Anisotropy Telescope - measured the very small scale fluctuations in small regions of the sky
• Boomerang - measured fluctuations with improved precision
• Maxima - measured fluctuations with improved precision
• Cosmic Background Imager - measured the very small scale fluctuations with improved precision in small regions of the sky
• Very Small Array - measured fluctuations with improved precision in small regions of the sky

Future instruments are expected to build upon WMAP's results. These include:

• Clover - improved precision and B-mode polarization measurements
• Planck Surveyor - improved precision at all angular scales over the whole sky

• WMAP Cold Spot
• Aitoff_projection

• WMAP Website at NASA GSFC

v • d • e Cosmic microwave background experiments
Space based experiments	RELIKT-1 · COBE · WMAP · Planck · SPOrt
Balloon experiments	QMAP · Saskatoon · MAXIMA · BOOMERanG · Archeops Spider
Ground based experiments	MAT · COSMOSOMAS · Tenerife Experiment · DASI · CBI · CAT · ACBAR · CAPMAP VSA · QUaD · SPT · SZA · ACT · AMI · Clover

v • d • e Space telescopes
Great Observatories program	Hubble Space Telescope  · Compton Gamma-Ray Observatory  · Chandra X-ray Observatory  · Spitzer Space Telescope
NASA	Swift Gamma-Ray Burst Mission  · Wilkinson Microwave Anisotropy Probe
European Space Agency	COROT  · INTEGRAL  · XMM-Newton
Other countries	ASTRO-E (Japan)
Future telescopes	Gamma-ray Large Area Space Telescope (2008)  · Herschel Space Observatory (2008)  · Kepler Mission (2009)  · Wide-field Infrared Survey Explorer (2009)  · NuSTAR (2011)  · Gaia mission (2011)  · James Webb Space Telescope (2013)  · New Worlds Mission (2013)  · Space Interferometry Mission (2015)  · Darwin Mission (2015)  · Laser Interferometer Space Antenna (2015)  · Terrestrial Planet Finder (TBD)
Completed missions	Cosmic Background Explorer  · Einstein Observatory  · Far Ultraviolet Spectroscopic Explorer  · IRAS  · Infrared Space Observatory  · AKARI
Canceled telescopes	Eddington mission